Fume hoods for laboratories



May 12,1959 H.. D. BYROWN 2,885,947

' FUME HOODS FOR'L'ABORATORIES Filed March 29, 195"! 1 2 Sheets-Sheet 1 I ATTORNEY H. D. BROWN FUME HOODS FOR LABORATORIES May 12, 1959 2 Sheets-Sheet 2 Filed March 29 1957 Fig. 3

49 I6 I4 is 33 4e 36 37 INVENTOR.

Harry D. Brown BY Fig. 4

ATTORNEY United States Patent M This invention relates to withdrawing fumes from a laboratory table. In certain classes of laboratory work, more particularly in the sampling of radioactive ores such as provide an open sample-receiving opening 14 therein. The sample cups, indicated at 15, are placed upon removable sample trays 16 extending longitudinally of the opening 14 in the table top and supported by the frame 12. The wall 10 is covered rearwardly of the table top by means of a backing plate 17 extending to a height of approximately twice the width of the table top.

An arcuately formed fume hood 18 extends from the top of the backing plate 17 forwardly and downwardly, terminating in an upturned channel gutter 19 in vertically spaced relation to the forward edge of the table top 13. End plates 20 close the ends of the hood 18 and extend downwardly to close the ends of the areas above uranium, the ore samples are placed in sample cups and immersed in acids and various reagents. The resulting fumes are exceedingly disagreeable and dangerous to the laboratory technicians, and if the usual types of exhaust fans are placed over the sample tables, the relatively great amount of air exhausted from the laboratory through the exhaust fans renders it difficult to properly heat and air condition the laboratory.

The principal object of this invention is to provide means for withdrawing fumes from a laboratory table which will rapidly and completely withdraw and discharge the fumes from the samples without interfering materially with the air conditioning or heating of the laboratory, and which will create a descending curtain of air between the samples and the laboratory to prevent substantial intermixture of the fumes and laboratory air, and to provide a rearward circulation of air over the samples to remove the fumes therefrom and from the laboratory without materially adding to or detracting from the natural atmospheric air of the laboratory.

A still further object is to provide a fume exhaust structure which will prevent the accumulation of condensed corrosive vapors, and which will prevent the formation of eddy currents in the air flow so as to reduce fall out or deposits of solid or fluid materials in the air flow channels.

Other objects and advantages reside in the detail construction of the invention, which is designed for simplicity, economy, and efficiency. These will become more apparent from the following description.

In the following detailed description of the invention, reference is had to the accompanying drawing which forms a part hereof. Like numerals refer to like parts in all views of the drawing and throughout the description.

In the drawing:

Fig. 1 is a front view of the improved laboratory table, with the fume-removing features of this invention applied thereto.

Fig. 2 is a vertical cross-section through the structure of Fig. 1, taken on the line 2--2, Fig. 1.

Fig. 3 is a perspective view of the improved laboratory table viewed from the interior of the laboratory, and

Fig. 4 is a perspective view of the improved laboratory table with a section thereof being cut away along a vertical plane taken perpendicular to the laboratory wall.

The invention is illustrated applied to a laboratory wall, as indicated at 10 and to a conventional laboratory table 11 supported upon a suitable supporting frame 12 positioned against the inside face of the wall 10. The table 11 may have any desired construction, as illustrated, the table is provided with a table top 13 which conveniently protrudes forwardly from the supporting frame 12. The table top 13 covers the full width of the table at each extremity, but is cut away at the mid-portion to the extremities of the table top 13. The end plates and fume hood are supported by means of suitable supports 21.

This invention contemplates forming ventilating opening 22 in the backing plate 17 extending the full height of the fume hood 18 and terminating above and in spaced relation to the table top 13 to form a relatively low back stop 23 rearwardly of the sample opening 14. A side plate 24 extends rearwardly from each side of the opening 22 and through the wall 10.

A hood-like, curvated air deflector plate 25 extends between the side plates 24 and joins the rear of the fume hood 18 over the opening 22. The air deflector plate extends rearwardly through the wall 10 and outwardly and downwardly therefrom at an angle of approximately 30 from the horizontal, thence curves vertically downward to form the rear wall of an air intake box 26.

A curvated throat plate 27 extends between the side plates 24 to form the front wall of the intake box 26, thence extends upwardly and forwardly toward the de flector plate 25 to form a restricted air passage therebetween, as indicated at A in Fig. 2. From the restricted passage A the throat plate 27 curves forwardly and downwardly on the circumference of a substantially circular arc to gradually increase the width of the air passageway between the fume hood 18 and the throat plate 27, as indicated at B in Fig. 2. The throat plate then inclines downwardly and rearwardly on a continuous smooth V curve to form an upper wall 28 in a horizontally elongated exhaust spout 29 having a rectangular cross-section.

A bottom plate 30 in the exhaust spout 29 extends forwardly and upwardly at a flaring angle to thewall 28 to form a horizontally elongated intake throat 31 for the exhaust spout 29. The bottom plate thence curves on a smooth continuous arc downwardly to form a vertical back wall 32 in spaced relation to the back stop 23, thence curves upwardly against the rear of the back stop 23 to form a condensate trough 33 along the lower edge of the back stop 23.

A horizontally elongated intake sleeve 34, shaped to correspond to the shape of the exhaust spout 29, is secured to the latter by means of suitable connecting flanges 35. The sleeve 34 discharges into the top of a collecting box 36 from one side of which air is drawn through a suction conduit 37 to the intake of an exhaust blower 38. The blower is driven by a suitable electric motor 39 and discharges into a suitable fume exhaust stack 40.

A first condensate drain 41 leads from the trough 33; a second condensate drain 42 leads from the collecting box 36; and a third condensate drain 43 leads from the housing of the exhaust blower 38. A filter pad, such as a glass fiber pad 44, is positioned in the intake box 26. The filter pad 44 serves to prevent dust, sand, and foreign materials from entering the air stream, and condensation on the walls of the various ducts and chambers is continuously removed by the condensate drains 41, 42, and 43. An arcuate shield plate 45 is secured to and arches downwardly between the front and rear plates of the intake box 26 to prevent atmospheric winds from blowing Patented May 12, 1959 air directly into the intake box. Both ends of the shield plate are open to provide semi-circular air intakes 46.

The height of the channel gutter 19 above the table top 13 is substantially two-thirds the Width of the throat opening, shown at B. The throat openings at A, B, and 31, and the capacity of the blower 38, are so proportioned that the air entering through the air intakes 46 will be completely withdrawn through the throat 31. The amount of air can be accurately controlled by means of adjustable louvers 47 positioned in an auxiliary intake sleeve 48 on the collecting box 36. The louvers can be controlled from a control rod 49 at the attendants position to accurately control the amount of air being Withdrawn through the throat 31 by limiting the amount drawn through the louvers 47.

When in use there is a continuous air flow, as shown by the arrows in Fig. 2. This air flow creates a descending curtain of air forwardly of the sample cups 15. This air then flows rearwardly over the top of the cups 15 and into the throat 31 so as to withdraw the fumes, as indicated in Fig. 2. This downwardly moving curtain of air at the open front below the hood 18 may create eddy currents in the air of the laboratory room, as indicated at C in Fig. 2, but if the laboratory room is maintained in normally closed condition to preclude drafts, air will be drawn therefrom only to a limited extent, since a substantial quantity of air is continuously admitted through passage A with no substantial withdrawal of air from the room and no discharge of air into the room.

It is recognized that there will be a certain amount of air drawn from the room through the front opening, and also through the slots in the table, but this amount of air is substantially less than would otherwise be the case in the absence of the hood and the inlet structure above described.

While a specific form of the improvement has been described and illustrated herein, it is to be understood that the same may be varied, within the scope of the appended claims, without departing from the spirit of the invention.

Having thus described the invention, what is claimed and desired secured by Letters Patent is:

1. Means for conducting fumes from a laboratory table and through the wall of a laboratory comprising: means forming an air exhaust throat extending through said wall slightly above the level of said table for conducting air rearwardly over the table and outwardly through the wall; means forming an intake air passage extending inwardly through the wall above said air exhaust throat and terminating above the table and above said throat, said intake passage exceeding the exhaust throat in mean cross-sectional area; means for directing air entering said intake passage downwardly over said table; means for drawing air outwardly through said exhaust throat to cause an inward and downward draft through said air passage; and a curvated throat plate forming the top in said exhaust throat thence curving inwardly, upwardly and outwardly to form the bottom in said intake air passage, so that air entering the intake air passage can flow on a continuous arcuate path about said curvated throat plate from said intake to said discharge passage above said table.

2. Means for conducting fumes from a laboratory as described in claim 1 having a curvated bottom plate extending from and rearwardly of said table upwardly and thence outwardly and downwardly on an arcuate curve and forming a bottom in said exhaust throat.

3. Means for conducting fumes from a laboratory table and through the wall of a laboratory comprising: means forming an air exhaust throat extending through said Wall slightly above the level of said table for drawing air rearwardly over the table and outwardly through the wall; means forming an intake air passage extending inwardly through the wall above said air exhaust throat and terminating above the table and above said throat, said intake passage exceeding the exhaust throat in mean cross-sectional area; a hood overlying said intake air passage; a collecting box, said exhaust throat being sealed to and discharging into said collecting box; fan means withdrawing air from said collecting box to cause an in ward and downward draft through said air passage; an auxiliary air inlet to said collecting box; and means for controlling the air entering said auxiliary inlet to control the amount of air entering said intake air passage.

References Cited in the file of this patent UNITED STATES PATENTS 1,131,192 White Mar. 9, 1915 1,934,808 Liptay Nov. 22, 1930 1,969,565 Klemme Aug. 7, 1934 2,227,481 Bates Jan. 7, 1941 2,341,245 Sonntag Feb. 8, 1944 

